The invention relates to a method of and apparatus for detecting ground faults in floating, i.e. ungrounded, electrical systems.
Ground fault detective apparatus must be capable of detecting not only faults on one or the other side of an electrical system, but also faults occurring simultaneously on both sides of the system. If such faults are more or less equally balanced, the difficulty of detecting the faults increases.
One prior art method of detecting balanced ground faults known to me is described in U.S. Pat. No. 3,754,221. The method comprises the location of a fault in one side of a circuit by connecting a resistance of known value to the opposite side of the circuit, grounding such resistance through a voltage detector and determining the voltage drop. More specifically, the method comprises repeating the above step alternately for opposite sides of the circuit to provide a measurement of faults in both sides of the circuit.
The present invention proposes a novel approach and solution to the problem outlined above.
According to the present invention a method of detecting ground faults in ungrounded equipment having an electrical supply comprises the steps of;
Connecting either side of the supply to a chassis ground terminal of the equipment; PA1 Impressing a voltage varying alternately between two predetermined values on the terminal relative to one side of the supply; PA1 Detecting and monitoring, with respect to this side of the supply, the resulting potential between this side and the chassis ground, said potential varying between predetermined magnitudes in the absence of any ground leak, and PA1 Monitoring said potential, ground faults in the equipment being detectable by a change in magnitude of said varying potential, establishing ground faults by changes in the magnitude of the varying potential and PA1 Locating the faults with respect to the sides of the supply from variations to the upper and lower predetermined values.
In one form of the invention a predetermined value and substantially nil constitute the two values of voltage impressed on the chassis ground terminal.
Other aspects of the invention will become apparent from the following description of the apparatus and method according to the invention which is made by way of example only and with reference to the accompanying drawings.